feat(filter): allow filtering of an object

Allow ng.filter to filter an object as well as an array. Before, an
object would need to be converted into an array before filtering.

Closes #2694.
Ooops ! I was tricked by github's hiding 2 lines in between. I was reading:
> That's equivalent to the simple substring match with a `string`
   not containing "M".

So, it's fine as it is :)